1. Field of the Invention
This invention is directed generally to a medical diagnostic device that use Doppler ultrasound for obstetrical and vascular monitoring applications, and more specifically, to a doppler ultrasound bell that is attachable to an acoustic stethoscope.
2. Description of the Prior Art
Doctors, paramedics, nurses, etc. have used stethoscopes for years to transmit sounds such as, for example, heart sounds, via a column of air from a patient being examined to the human ear. Stethoscopes are used to evaluate the cardiac and respiratory systems by allowing the user to distinguish the sounds that the beating heart generates, as well as the sounds of gas exchange in the lungs. The quality of the sounds denotes whether the organ in the patient being examined is healthy or unhealthy. A stethoscope can also be used to measure arterial blood pressure in a patient's arm or leg.
A conventional acoustic stethoscope generally includes two flexible rubber tubes connected to eartips or ear pieces at one end and a chest piece at the other end. The chest piece usually includes turret attached to at least one bell shaped cone that transmits low-pitched sounds via a column of air to the eartips or a diaphragm that transmits high-pitched sounds via a column of air to the eartips. The turret on a chestpiece will often include threads so that acoustic bells or diaphragms of different sizes and shapes can be attached to and removed from the stethoscope, thereby increasing the versatility of the stethoscope. In addition, many of the turrets on many conventional acoustic stethoscopes are capable of simultaneous attachment to multiple diaphragms or bells, further increasing the versatility of the acoustic stethoscope. Furthermore, electronic stethoscopes have been developed which amplify the sounds generated through the bell or diaphragm so as to improve the diagnostic capabilities of the user. For example, U.S. Pat. No. 3,247,324 issued to Cefaly et al., U.S. Pat. No. 4,618,986 issued to Hower; and U.S. Pat. No. 4,783,813 issued to Kempka disclose electronic stethoscopes.
In addition to stethoscopes, the diagnostic capabilities of the medical profession have increased significantly throughout the years. Two such advancements have been in the use of Doppler ultrasound based devices to detect and measure vascular and cardial blood flow direction and rate, to detect and measure fetal heart rate, and for numerous other diagnostic applications.
The basic Doppler effect for sound is well-known. When a source of sound and a receiver of the sound move in relation to each other, the pitch or frequency of the sound perceived or detected at the receiver is different from the pitch or frequency of the source. If they are moving toward each other, the perceived or received pitch or frequency of the sound is higher than the source sound. The classic example is standing near a railroad track as a train blowing its whistle passes. As the train approaches, the perceived whistle sound is a high pitch, which then changes abruptly to a lower pitch as the train passes and goes away from the listener.
Ultrasound is simply sound that has a higher pitch or frequency than the hearing capability of a normal human ear, which is about twenty kilohertz (20 KHz). The Doppler effect for ultrasound is the same as for audible sound, but, since ultrasound is at a pitch or frequency beyond the range of human ears, electronic equipment is used to detect it.
The Doppler effect is also produced in echoes, when sound or ultrasound is reflected by, or bounced off, a moving object. Thus, sound or ultrasound can be produced and projected by a speaker device or ultrasound sender, and, if it reflects or bounces off an object or target, the echo or return sound can be received and detected. If the ultrasound source, target object, and echo receiver are all stationary, the pitch or frequency of the echo ultrasound will be the same as the source ultrasound. However, if the target object is moving toward the receiver of the ultrasound echo, the ultrasound echo received and detected will have a higher pitch than if the target object was moving away from the receiver. The speed or velocity at which the target object is moving toward or away from the receiver determines the pitch or frequency of the echo received. Also, a fluid, such as blood, also reflects ultrasound waves, and the velocity or rate of blood flow determines the frequency of the echoed ultrasound waves. Thus, detecting frequencies of the echoed ultrasound waves can be used to measure direction and rate of blood flow. This Doppler effect in echoed ultrasound is the principle that is typically utilized in ultrasound medical diagnostic devices, where ultrasound signals having frequencies in the range between one (1) megahertz (MHz) and twenty (20) MHz are often used.
In medical diagnostic devices using Doppler ultrasound, the source of the ultrasound and the receiver of the ultrasound are usually transducers mounted in a hand-held probe. The probe is held relatively stationary with respect to a target object being detected or measured. Some slow movement and positioning of the probe by the physician or technician can be accommodated for detecting, if it is substantially slower than the motion of the target object. However, where accurate measurements are needed, the probe should be held quite stationary. An ultrasound wave stream is transmitted by the transducer in the probe in the direction of the target object to be detected or measured, and after the reflected ultrasound wave is received, an electric signal is created by a transducer that has both a frequency and an amplitude that corresponds to the frequency and amplitude of the reflected ultrasound waves. For example, in obstetrical applications, such as detecting or measuring fetal heart rate, the ultrasound waves from the probe are directed so as to intercept the blood flowing in a beating fetal heart. In vascular applications, the ultrasound waves from the probe are directed to intercept blood moving and circulating in a vein or artery to detect or measure blood flow and direction. In both situations, the directed signal from the probe is reflected by the flowing blood, which creates Doppler shifts from the frequency of the ultrasound by the probe to the frequencies of the echoed ultrasound reflected from the flowing blood. The reflected ultrasound waves from the flowing blood is detected by a transducer in the probe, which converts ultrasound waves energy to electric signals. The Doppler frequency shift between the directed ultrasound and the reflected ultrasound waves returned from the flowing blood varies proportionally with the instantaneous velocity of the flowing blood. If the blood is flowing away from the directed ultrasound from the probe, the reflected ultrasound waves will lower frequencies than the directed ultrasound. If the blood is flowing toward the directed ultrasound from the probe, the reflected ultrasound waves will have higher frequencies than the directed ultrasound. Of course, if the moving target is not moving in relation to the directed ultrasound from the probe, the reflected ultrasound wave will have the same frequency as the directed ultrasound.
Doppler ultrasound techniques for medical diagnostic purposes are well known in the art. For example, see Peter Atkinson & John Woodcock, DOPPLER ULTRASOUND AND ITS USE IN CLINICAL MEASUREMENT, published by Academic Press of New York City (1982); Matthew Hussey, BASIC PHYSICS AND TECHNOLOGY OF MEDICAL DIAGNOSTIC UULTRASOUND, published by Elsevier of New York City (1985); and Peter Fish, PHYSICS AND INSTRUMENTATION OF DIAGNOSTIC MEDICAL ULTRASOUND, published by John Wiley & Sons of New York City (1990). See also, U.S. Pat. No. 4,276,491 issued to Daniel; U.S. Pat. No. 4,807,636 issued to Skidmore et al.; U.S. Pat. No. 4,850,364 issued to Leavitt; and U.S. Pat. No. 5,394,878 issued to Frazin all of which show medical devices using Doppler ultrasound techniques. Furthermore, Doppler ultrasound has become a popular method of medical diagnosis because it is non-invasive, painless, creates little or no side effects, and is relatively inexpensive. Finally, ultrasound frequencies are often used in medical diagnostic applications because they reflect well from the boundaries between different organs and blood cells without utilizing potentially harmful ionizing radiation.
In many medical diagnostic applications using Doppler ultrasound, the transmitter of the directed signal is placed directly against the human skin. For example, when measuring fetal heart rate, the transmitter is placed on the midline of the abdomen and aimed downward toward the pubic bone. When measuring vascular flow, the transmitter is placed directly over the underlying vessel. The direct contact between the transmitter and the human skin is necessary to reduce reflections of the directed ultrasound and the reflected ultrasound echo caused by the skin, and ultrasound does not propagate well in air at the frequencies used in these applications. To facilitate ease of use and manual manipulation of diagnostic devices using Doppler ultrasound, as described above, it is desirable to have a device that is small, portable, and battery operated, since the probe must often be placed directly next to the skin of the patient being tested.
The use of Doppler ultrasound has gained wide acceptance in the medical profession. Furthermore, ultrasound probes that are attachable to the flexible rubber ear tubes that are a part of conventional stethoscopes are known in the art. For example, the Doplette.TM. doppler device manufactured by Imex Medical Systems, Inc., of Golden, Colo., allows an ultrasound transmitter and receiver to be removably connected to the ear tubes from a conventional acoustic stethoscope. The Doplette.TM. doppler device, however, requires that the chestpiece and turret of the stethoscope be removed so that the Doplette.TM. doppler device can be attached directly to the flexible hose or tube. The Mascot.TM. system, also manufactured by Imex Medical Systems, allows a doppler ultrasound probe to be interchanged with an electronic stethoscope probe. The Mascot.TM. system, however, functions as an electronic stethoscope and requires that the ultrasound probe be removed when the stethoscope probe is being used, and vice-versa.
Despite the well developed state of the art in both stethoscope and ultrasound devices, there remains a need for an ultrasound probe or bell to be attachable to the turret of a conventional acoustic stethoscope and, more specifically, a need for the capability of simultaneously attaching an ultrasound bell and an acoustic bell or diaphragm to a conventional acoustic stethoscope.